1. Field of the Invention
The invention relates to a fan control device, more particularly to a fan control device with a breakdown warning capability so as to be capable of shutting down a fan and of generating a warning signal upon detecting that the fan speed is abnormally slow, indicative of a near-breakdown condition.
2. Description of the Related Art
After operating for a period of time, an electrical appliance, such as a desktop computer, a notebook computer, a server or an uninterruptible power system, generates heat that causes the internal temperature of the electrical appliance to rise. This increase in temperature can lead to malfunctioning of the electrical appliance that, in some cases, can result in loss of data and even in damage to electronic components of the appliance. In order to dissipate heat quickly from the interior of the electrical appliance, a heat-dissipating device, such as a fan, is usually installed inside the appliance.
A conventional low-cost heat-dissipating fan commonly found in electrical appliances has two input wires to be connected to positive and negative terminals of a power supply. When the appliance is activated, power is supplied to operate the fan. When the appliance is deactivated, power is cut-off to stop operation of the fan. However, when breakdown of the fan has occurred and is not detected in time, malfunctioning of the electrical appliance can still occur and can result in loss of data and even in damage to electronic components of the appliance.
It has been observed that, before the fan comes to a full stop due to breakdown, the speed of the fan gradually decreases from the normal operating speed. As such, whether or not breakdown of the fan is about to occur can be determined by observing the speed of the fan. To this end, another conventional heat-dissipating fan has been developed to incorporate two power input wires for connection to positive and negative terminals of a power supply, and a clock output wire that provides a clock output corresponding to the speed of the fan. That is, when the fan operates at a relatively fast speed, a high-speed clock output is generated at the clock output wire. Accordingly, when the fan operates at a relatively slow speed, a low-speed clock output is generated at the clock output wire. Thus, by observing the speed of the clock output, one can determine whether or not breakdown of the fan is about to occur so that replacement of the fan can be conducted.
However, because of the relatively high cost of the conventional three-wire heat-dissipating fan, most electrical appliances, such as desktop computers, notebook computers, servers and uninterruptible power systems, still use the conventional two-wire heat-dissipating fan described beforehand.